[Leetcode] invalid Ric tree

Given a binary tree, check whether it is a mirror of itself (ie, shortric around its center ).

For example, this binary tree is unsupported Ric:

    1   /   2   2 / \ / 3  4 4  3

 

But the following is not:

    1   /   2   2   \      3    3

 

Note:
Bonus points if you cocould solve it both recursively and iteratively.

Solution 1: recursive

 1 /** 2  * Definition for binary tree 3  * public class TreeNode { 4  *     int val; 5  *     TreeNode left; 6  *     TreeNode right; 7  *     TreeNode(int x) { val = x; } 8  * } 9  */10 public class Solution {11     public boolean isSymmetric(TreeNode root) {12         if (root == null)13             return true;14         return mySymmetric(root.left,root.right);15         16     }17 18     private boolean mySymmetric(TreeNode left, TreeNode right) {19         // TODO Auto-generated method stub20         if(left==null&&right==null)21             return true;22         if(left==null||right==null)23             return false;24         return (left.val==right.val)&&mySymmetric(left.right, right.left)&&mySymmetric(left.left, right.right);25     }26 }

 

Solution 2: iterative

 1 /** 2  * Definition for binary tree 3  * public class TreeNode { 4  *     int val; 5  *     TreeNode left; 6  *     TreeNode right; 7  *     TreeNode(int x) { val = x; } 8  * } 9  */10 public class Solution {11     public boolean isSymmetric(TreeNode root) {12         //iterative way13         if(root==null)14             return true;15         Stack<TreeNode> sl=new Stack<TreeNode>();16         Stack<TreeNode> sr=new Stack<TreeNode>();17         sl.add(root.left);18         sr.add(root.right);19         while(!sl.isEmpty()&&!sr.isEmpty()){20             TreeNode n1=sl.pop();21             TreeNode n2=sr.pop();22             if(n1==null&&n2==null)23                 continue;24             if(n1==null||n2==null)25                 return false;26             if(n1.val!=n2.val)27                 return false;28             sl.push(n1.left);29             sl.push(n1.right);30             sr.push(n2.right);31             sr.push(n2.left);32         }33         return true;34     }35 }

 

[Leetcode] invalid Ric tree